Potassium and Argon data for dating the core, and radiochemical data of a series of measurements made on layers inside various manganese nodules from the Pacific Ocean

Although various models have been proposed to explain the origin of manganese nodules (see Goldberg and Arrhenius), two major hypotheses have received extensive attention. One concept suggests that manganese nodules form as the result of interaction between submarine volcanic products and sea water. The common association of manganese nodules with volcanic materials constitutes the main evidence for this theory. The second theory involves a direct inorganic precipitation of manganese from sea water. Goldberg and Arrhenius view this process as the oxidation of divalent manganese to tetravalent manganese by oxygen under the catalytic action of particulate iron hydroxides. Manganese accumulation by the Goldberg and Arrhenius theory would be a relatively slow and comparatively steady process, whereas Bonatti and Nayudu believe manganese nodule formation takes place subsequent to the eruption of submarine volcanoes by the acidic leaching of lava.

Miocene to Pleistocene gluconite-rich layers of the US Mid-Atlantic margin

Glauconite is generally agreed to be a reliable indicator of low sedimentation rate, but little systematic work has been done to specify the role of glauconite in a sequence-stratigraphic framework. Ocean Drilling Program Leg 174A recovered a good record of late Tertiary sediments along the shelf edge of the New Jersey US Atlantic margin, and glauconite was present in many intervals of the cores, sometimes in vertical proximity to sequence boundaries. Leg 174A glauconite was analyzed with binocular microscope, XRD and SEM to determine the percent of potassium and degree of maturity in order to relate occurrence to depositional environment. Seismic data were used to locate sequence boundaries, and percent glauconite was visually estimated. Glauconite samples from Site 1073 were found to have formed within a lowstand systems tract (LST), and as part of a distal condensed section (CS) within a transgressive systems tract (TST). These results are comparable to those from nearby Site 903 of Leg 150, which indicate a similar depositional setting for glauconite. Glauconites at shelf Sites 1071 and 1072 likely formed in the TST as well. Onshore, glauconite occurs mainly in transgressive systems tracts. The Miocene appears to be the upper limit of glauconite formation onshore. As the magnitude of sea-level change decreased, present onshore locations became too nearshore to maintain sediment-free environments, and the zone of glauconite deposition moved seaward. The same process did not occur offshore until the Plio-Pleistocene. Low subsidence-rate margins such as the US Atlantic are subject more to the variations of sea-level than to changes in sediment supply, tectonics, or other factors influencing their depositional patterns. Although glauconite occurrence is widespread in the stratigraphic record, this study demonstrates that for low subsidence-rate margins, primary deposition of glauconite is largely restricted to the TST.

Warmer, deeper and greener mixed layers in the north Atlantic subpolar gyre over the last 50 years.

Shifts in global climate resonate in plankton dynamics, biogeochemical cycles, and marine food webs. We studied these linkages in the North Atlantic subpolar gyre (NASG), which hosts extensive phytoplankton blooms. We show that phytoplankton abundance increased since the 1960s in parallel to a deepening of the mixed layer and a strengthening of winds and heat losses from the ocean, as driven by the low frequency of the North Atlantic Oscillation (NAO). In parallel to these bottom-up processes, the top-down control of phytoplankton by copepods decreased over the same time period in the western NASG, following sea surface temperature changes typical of the Atlantic Multi-decadal Oscillation (AMO). While previous studies have hypothesized that climate-driven warming would facilitate seasonal stratification of surface waters and long-term phytoplankton increase in subpolar regions, here we show that deeper mixed layers in the NASG can be warmer and host a higher phytoplankton biomass. These results emphasize that different modes of climate variability regulate bottom-up (NAO control) and top-down (AMO control) forcing on phytoplankton at decadal timescales. As a consequence, different relationships between phytoplankton, zooplankton, and their physical environment appear subject to the disparate temporal scale of the observations (seasonal, interannual, or decadal). The prediction of phytoplankton response to climate change should be built upon what is learnt from observations at the longest timescales.

Warmer, deeper and greener mixed layers in the north Atlantic subpolar gyre over the last 50 years.

Shifts in global climate resonate in plankton dynamics, biogeochemical cycles, and marine food webs. We studied these linkages in the North Atlantic subpolar gyre (NASG), which hosts extensive phytoplankton blooms. We show that phytoplankton abundance increased since the 1960s in parallel to a deepening of the mixed layer and a strengthening of winds and heat losses from the ocean, as driven by the low frequency of the North Atlantic Oscillation (NAO). In parallel to these bottom-up processes, the top-down control of phytoplankton by copepods decreased over the same time period in the western NASG, following sea surface temperature changes typical of the Atlantic Multi-decadal Oscillation (AMO). While previous studies have hypothesized that climate-driven warming would facilitate seasonal stratification of surface waters and long-term phytoplankton increase in subpolar regions, here we show that deeper mixed layers in the NASG can be warmer and host a higher phytoplankton biomass. These results emphasize that different modes of climate variability regulate bottom-up (NAO control) and top-down (AMO control) forcing on phytoplankton at decadal timescales. As a consequence, different relationships between phytoplankton, zooplankton, and their physical environment appear subject to the disparate temporal scale of the observations (seasonal, interannual, or decadal). The prediction of phytoplankton response to climate change should be built upon what is learnt from observations at the longest timescales.

Production of Highly Monolayer Enriched Dispersions of Liquid-Exfoliated Nanosheets by Liquid Cascade Centrifugation

While liquid exfoliation is a powerful technique to produce defect-free nanosheets in large quantities, its usefulness is limited by broad nanosheet thickness distributions and low monolayer contents. Here we demonstrate liquid processing techniques, based on iterative centrifugation cascades, which can be designed to achieve either highly efficient nanosheet size-selection and/ or monolayer enrichment. The resultant size-selected dispersions were used to establish quantitative metrics to determine monolayer volume fraction, as well as mean nanosheet size and thickness, from standard spectroscopic measurements. Such metrics allowed us to design and optimize centrifugation cascades to enrich liquid exfoliated WS2 dispersions up to monolayer contents of 75%. Monolayer-rich dispersions show relatively bright photoluminescence with narrow line widths (

Layers of Listening: Qualitative Analysis of the Impact of Early Intervention Services for First-episode Psychosis on Carers' Experiences

Background Early intervention services (EIS) comprise low-stigma, youth-friendly mental health teams for young people undergoing first-episode psychosis (FEP). Engaging with the family of the young person is central to EIS policy and practice. Aims By analysing carers' accounts of their daily lives and affective challenges during a relative's FEP against the background of wider research into EIS, this paper explores relationships between carers' experiences and EIS. Method Semi-structured longitudinal interviews with 80 carers of young people with FEP treated through English EIS. Results Our data suggest that EIS successfully aid carers to support their relatives, particularly through the provision of knowledge about psychosis and medications. However, paradoxical ramifications of these user-focused engagements also emerge; they risk leaving carers' emotions unacknowledged and compounding an existing lack of help-seeking. Conclusions By focusing on EIS's engagements with carers, this paper draws attention to an urgent broader question: as a continuing emphasis on care outside the clinic space places family members at the heart of the care of those with severe mental illness, we ask: who can, and should, support carers, and in what ways?

Quantitative characterization of physico-chemical properties of the active layers of reverse osmosis and nanofiltration membranes, and their relation to membrane performance

The main objectives of this dissertation were: (i) to develop experimental and analytical procedures to quantify different physico-chemical properties of the ultra-thin (~ 100 nm) active layers of reverse osmosis (RO) and nanofiltration (NF) membranes and their interactions with contaminants; (ii) to use such procedures to evaluate the similarities and differences between the active layers of different RO/NF membranes; and (iii) to relate characterization results to membrane performance. Such objectives were motivated by the current limited understanding of the physico-chemical properties of active layers as a result of traditional characterization techniques having limitations associated with the nanometer-scale spatial resolution required to study these ultra-thin films. Functional groups were chosen as the main active layer property of interest. Specific accomplishments of this study include the development of procedures to quantify in active layers as a function of pH: (1) the concentration of both negatively and positively ionized functional groups; (2) the stoichiometry of association between ions (i.e., barium) and ionized functional groups (i.e., carboxylate and sulfonate); and (3) the steric effects experienced by ions (i.e., barium). Conceptual and mathematical models were developed to describe experimental results. The depth heterogeneity of the active layer physico-chemical properties and interactions with contaminants studied in this dissertation was also characterized. Additionally, measured concentrations of ionized functional groups in the polyamide active layers of several commercial RO/NF membranes were used as input in a simplified RO/NF transport model to predict the rejection of a strong electrolyte (i.e., potassium iodide) and a weak acid (i.e., arsenious acid) at different pH values based on rejection results at one pH condition. The good agreement between predicted and experimental results showed that the characterization procedures developed in this study serve as useful tools in the advancement of the understanding of the properties and structure of the active layers of RO/NF membranes, and the mechanisms of contaminant transport through them.

Nanofiltration membranes modified with aromatic polyamide dendrimers active layers

This thesis describes the modification of the commercial TFC-S nanofiltration membrane with shape-persistent dendritic architectures. Amphiphilic aromatic polyamide dendrimers (G1-G3) are synthesized via a divergent approach and used for membrane modification by direct percolation. The permeate samples collected from the percolation experiments are analyzed by UV-Vis spectroscopy to instantly monitor the influence of dendrimer generations on percolation behaviors and new active layer formation. The membrane structures are further characterized by Rutherford backscattering spectrometry (RBS) and atomic force microscopy (AFM) techniques, suggesting a low-level accumulation of dendrimers inside the TFC-S NF membranes and subsequent formation of an additional aramide dendrimer active layer. Thus, all the modified TFC-S membranes have a double active layer structure. A PES-PVA film is used as a control membrane showing that structural compatibility between the dendrimer and supports plays an important role in the membrane modification process. The performance of modified TFC-S membrane is evaluated on the basis of rejection abilities of a variety of water contaminants having a range of sizes and chemistry. As the water flux is inversely proportional to the thickness of the active layer, we optimize the amount of dendrimers deposited for specific contaminants to improve the solute rejection while maintaining high water flux.

Nonlinear Optics and Carrier Dynamics in Nanostructured and Two-Dimensional Materials

Understanding and measuring the interaction of light with sub-wavelength structures and atomically thin materials is of critical importance for the development of next generation photonic devices.  One approach to achieve the desired optical properties in a material is to manipulate its mesoscopic structure or its composition in order to affect the properties of the light-matter interaction.  There has been tremendous recent interest in so called two-dimensional materials, consisting of only a single to a few layers of atoms arranged in a planar sheet.  These materials have demonstrated great promise as a platform for studying unique phenomena arising from the low-dimensionality of the material and for developing new types of devices based on these effects.  A thorough investigation of the optical and electronic properties of these new materials is essential to realizing their potential.  In this work we present studies that explore the nonlinear optical properties and carrier dynamics in nanoporous silicon waveguides, two-dimensional graphite (graphene), and atomically thin black phosphorus. We first present an investigation of the nonlinear response of nanoporous silicon optical waveguides using a novel pump-probe method. A two-frequency heterodyne technique is developed in order to measure the pump-induced transient change in phase and intensity in a single measurement. The experimental data reveal a characteristic material response time and temporally resolved intensity and phase behavior matching a physical model dominated by free-carrier effects that are significantly stronger and faster than those observed in traditional silicon-based waveguides.  These results shed light on the large optical nonlinearity observed in nanoporous silicon and demonstrate a new measurement technique for heterodyne pump-probe spectroscopy. Next we explore the optical properties of low-doped graphene in the terahertz spectral regime, where both intraband and interband effects play a significant role. Probing the graphene at intermediate photon energies enables the investigation of the nonlinear optical properties in the graphene as its electron system is heated by the intense pump pulse. By simultaneously measuring the reflected and transmitted terahertz light, a precise determination of the pump-induced change in absorption can be made. We observe that as the intensity of the terahertz radiation is increased, the optical properties of the graphene change from interband, semiconductor-like absorption, to a more metallic behavior with increased intraband processes. This transition reveals itself in our measurements as an increase in the terahertz transmission through the graphene at low fluence, followed by a decrease in transmission and the onset of a large, photo-induced reflection as fluence is increased.  A hybrid optical-thermodynamic model successfully describes our observations and predicts this transition will persist across mid- and far-infrared frequencies.  This study further demonstrates the important role that reflection plays since the absorption saturation intensity (an important figure of merit for graphene-based saturable absorbers) can be underestimated if only the transmitted light is considered. These findings are expected to contribute to the development of new optoelectronic devices designed to operate in the mid- and far-infrared frequency range.  Lastly we discuss recent work with black phosphorus, a two-dimensional material that has recently attracted interest due to its high mobility and direct, configurable band gap (300 meV to 2eV), depending on the number of atomic layers comprising the sample. In this work we examine the pump-induced change in optical transmission of mechanically exfoliated black phosphorus flakes using a two-color optical pump-probe measurement. The time-resolved data reveal a fast pump-induced transparency accompanied by a slower absorption that we attribute to Pauli blocking and free-carrier absorption, respectively. Polarization studies show that these effects are also highly anisotropic - underscoring the importance of crystal orientation in the design of optical devices based on this material. We conclude our discussion of black phosphorus with a study that employs this material as the active element in a photoconductive detector capable of gigahertz class detection at room temperature for mid-infrared frequencies.